The word atom is another great science word created by scientists for scientific and philosophical use-only in this case it was Leucippus and Democritus 2500 years ago! Our word atom is a direct transliteration of the Ancient Greek word atomos combining the alpha privative a with the verb temnein meaning to cut, yielding the meaning indivisible particle, uncut. It is unclear whether the credit goes to Leucippus or Democritus, though most agree that the term really came to use under Democritus. The idea of the atom was known a few centuries earlier in India, and Lucretius followed with extensive writing on the subject.
It wasn’t until Antoine Lavoisier began his study of chemistry that elements were separated and the idea of the atom took its modern meaning and form. Shortly after Lavoisier, John Dalton published his paper on atomic structure and the search for the smallest units of matter was on. Dalton’s paper was followed quickly by Gay-Lussac and then immediately again by Amadeo Avagadro who took to measuring the weight of the atom in gases. Avagadro recognized that gases could occur as both atoms and molecules, something Dalton did not foresee. In 1865 Johann Josef Loschmidt measured the size of an atom and by the end of the century discoveries by JJ Thomspon and Rutherford gave a glimpse of the interior of the atom. Niels Bohr laid the groundwork for sub-atomic and quantum theory and was awarded the Nobel Prize for his studies. In 1926 Erwin Schrodinger published his paper proposing that the electron acted as much like a wave as it did matter.
Etching of Democritus from an ancient marble in the public domain.